Protein Phosphate in the Regulation of Protein Phosphorylation and Insulin Secretion
dc.contributor.advisor | Robert Easom | |
dc.contributor.committeeMember | Porunelloor Mathew | |
dc.contributor.committeeMember | Ming-Chi Wu | |
dc.creator | Parameswara, Vinay K. | |
dc.date.accessioned | 2019-08-22T21:15:28Z | |
dc.date.available | 2019-08-22T21:15:28Z | |
dc.date.issued | 2003-05-01 | |
dc.date.submitted | 2013-09-23T13:42:07-07:00 | |
dc.description.abstract | Parameswara, Vinay K., Protein Phosphatase 2A in the Regulation of Ca2+- Sensitive Protein Phosphorylation and Insulin Secretion. Doctor of Philosophy (Biomedical Sciences), May 2003; 191 pp., 28 illustrations; 5 tables; 250 references. Type 2 diabetes is characterized by insufficient insulin secretion in the midst of increased demand from concomitant insulin resistance of peripheral tissues. More specifically, the diabetic β-cell is characterized by impaired responsiveness to D-glucose, the primary physiological regulator of insulin secretion, necessitating that the mechanism of glucose-induced insulin secretion from the β-cell of the pancreas is critically dependent on an elevation of cytosolic calcium as a trigger signal but is also dependent on reversible protein phosphorylation. Accordingly, a number of protein kinases are activated by glucose, or by incretin hormones that enhance glucose-induced insulin secretion. This dissertation however stems from a general hypothesis that protein phosphorylation and insulin secretion may also be controlled via the regulation of protein phosphatases (PP). Initially, a panel of specific antibodies was used to profile the expression of known PP species in the β-cell. By immunoblotting cultured clonal β-cells, INS-1, were shown to express various protein phosphatases namely PP 1, 2A, 2B, 2C, 4 and 6, but with distinct subcellular localization suggesting that these phosphatases regulated distinct functions within the β-cells. Of particular interest, PP-2A holoenzyme was localized to purified fractions of insulin secretory granules suggesting an involvement in insulin regulation. Selective inhibition of PP-2A in the presence of endothall or low concentrations of okadaic acid, increased insulin secretion in the presence of glucose in INS-1 cells. In order to discern potential substrates of PP-2A and thus-mechanisms of action, microcystin immobilized to sepharose was employed to affinity purify phosphatase species from β-cell lysates and proteins complexed with them. Fractions containing PP-2A also contained synapsin I and a specific interaction of these proteins was confirmed by co-immunoprecipitation from INS-1 cell lysates. In contrast, PP-1 was not associated with synapsin I. That synapsin I is indeed a substrate for PP-2A in INS-1 cells was confirmed via the demonstration that synapsin I phosphorylation was increased by okadaic acid under conditions that increased insulin release. Okadaic acid also induced the autophosphrylation and activation of CaMKII, a Ca2+-dependent kinase that phosphorylates synapsin I; suggesting CaMKII may mediate PP-2A effects on insulin secretion. The elimination of syanpsin I, markedly modulates glucose homeostasis of mice and subtly modulates insulin release. In summary these studies document that the modulation of PP-2A in β-cells dramatically influences insulin secretion reinforcing a concept that the control of protein phosphatase may have a critical role in the regulation of insulin secretion. These data suggest that a role of PP-2A on insulin secretion is mediated in part through the regulation of CaMKII activity and synapsin I-phosphorylation. | |
dc.format.mimetype | application/pdf | |
dc.identifier.uri | https://hdl.handle.net/20.500.12503/29194 | |
dc.language.iso | en | |
dc.provenance.legacyDownloads | 0 | |
dc.subject | Cell and Developmental Biology | |
dc.subject | Cell Biology | |
dc.subject | Cells | |
dc.subject | Cellular and Molecular Physiology | |
dc.subject | Chemicals and Drugs | |
dc.subject | Diseases | |
dc.subject | Life Sciences | |
dc.subject | Medical Cell Biology | |
dc.subject | Medicine and Health Sciences | |
dc.subject | Nutritional and Metabolic Diseases | |
dc.subject | Protein phosphate 2A | |
dc.subject | regulation | |
dc.subject | Ca2+ | |
dc.subject | Protein phosphorylation | |
dc.subject | insulin secretion | |
dc.subject | type 2 Diabetes | |
dc.subject | glucose | |
dc.subject | β cell | |
dc.subject | synapsin I | |
dc.subject | okadaic acid | |
dc.subject | CaMKII | |
dc.title | Protein Phosphate in the Regulation of Protein Phosphorylation and Insulin Secretion | |
dc.type | Dissertation | |
dc.type.material | text | |
thesis.degree.department | Graduate School of Biomedical Sciences | |
thesis.degree.discipline | Biomedical Sciences | |
thesis.degree.grantor | University of North Texas Health Science Center at Fort Worth | |
thesis.degree.name | Doctor of Philosophy |
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